62 research outputs found
Bimodal fission of Hs*
No full textMass and energy distributions of fission fragments obtained in the reactions 22Ne + 249Cf, 26Mg + 248Cm, and 22Ne + 238U have been measured. A special attention will be paid on the properties of mass-energy distribution of fission fragments obtained in the reaction 26Mg + 248Cm at an excitation energy of 35 MeV. At this energy shell effects should become more effective in fission, the TKE distribution of symmetric fragments obtained in the reaction 26Mg + 248Cm differs strongly from a Gaussian shape. Besides a low-energy component, a high-energy component, not foreseen in the LDM, arises. This is attributed to the fact that both fission fragments are close to the spherical neutron shell N 82. It means that for the compound nucleus 274Hs*, formed in the reaction 26Mg + 248Cm, the phenomenon of bimodal fission was observed for the first time. For the compound nucleus 260No* formed in the reaction 22Ne + 238U at the initial excitation energy of 41 MeV the bimodal fission as well as superasymmetric fission were observed. © Published under licence by IOP Publishing Ltd.SCOPUS: cp.jinfo:eu-repo/semantics/publishe
Mass distributions for quasifission processes in superheavy compositesystems with Z=108-120
No full textThis paper presents the study of mass-energy distributions of quasifission fragments obtained in the reactions 36S, 48Ca, 64Ni+238U at energies below and above the Coulomb barrier. To describe the quasifission mass distribution the simple model has been proposed. This model is based on the driving potential of the system and time dependent mass drift. This procedure allows to estimate QF time scale from the measured mass distributions
Mass distributions for quasifission processes in superheavy compositesystems with Z=108-120
No full textThis paper presents the study of mass-energy distributions of quasifission fragments obtained in the reactions 36S, 48Ca, 64Ni+238U at energies below and above the Coulomb barrier. To describe the quasifission mass distribution the simple model has been proposed. This model is based on the driving potential of the system and time dependent mass drift. This procedure allows to estimate QF time scale from the measured mass distributions
Neutron emission in fission and quasi-fission of Hs
No full textMass and energy distributions of fission-like fragments obtained in the reactions 26Mg + 248Cm, 36S+ 238U and 58Fe + 208Pb leading to the formation of 266,274Hs are reported. From the analysis of TKE distributions for symmetric fragment it was found that at energies below the Coulomb barrier the bimodal fission of 274Hs, formed in the reaction 26Mg+ 248Cm, is observed, while in the reaction 36S+ 238U at these energies the main part of the symmetric fragments arises from the quasi-fission process. At energies above the Coulomb barrier the fusion-fission is a main process leading to the formation of symmetric fragment for the both reactions. In the case of 58Fe+ 208Pb reaction the quasi-fission process is the main reaction mechanism at all measured energies. The pre- and post-scission neutron multiplicities as a function of the fragment mass have been obtained for all studied reactions. © 2010 American Institute of Physics.SCOPUS: cp.pinfo:eu-repo/semantics/publishe
Is nuclear viscosity dependent on temperature?
No full textNuclear viscosity is an indispensable ingredient of the nuclear fission collective dynamical models. It governs the exchange of energy between the collective variables and the thermal bath. Its dependence on the shape and temperature is a matter of controversy. By using systems of intermediate fissility we have demonstrated in a recent study that the viscosity parameters is larger for compact shapes, and decreases for larger deformations of the fissioning system, at variance with the conclusions of the statistical model modified to include empirically viscosity and time scales. In this contribution we propose an experimental scenario to highlight the possible dependence of the viscosity from the temperature
Fusion-Fission of superheavy compound nuclei produced in reacions with heavy ions beyond Ca
No full textTotal Kinetic Energy - Mass distributions of fission-like fragments for the reactions of 22Ne, 26Mg, 36S, 48Ca, 58Fe and 64Ni ions with actinides leading to the formation of superheavy compound systems with Z=108-120 at energies near the Coulomb barrier have been measured. Fusion-fission cross sections were estimated from the analysis of mass and total kinetic energy distributions. It was found that the fusion probability drops by three orders of magnitude for the formation of the compound nucleus with Z=120 obtained in the reaction 64Ni+238U compared to the formation of the compound nucleus with Z=112 obtained in the reaction 48Ca+238U at the excitation energy of the compound nucleus of about 45 MeV. From our analysis it turns out that the reaction 64Ni+238U is not suitable for the synthesis of element Z=120
Fusion suppression in mass-asymmetric reactions leading to Ra compound nuclei
No full textNear-barrier excitation functions have been measured for evaporation-residue production and fission in the 12C+204,206,208Pb and 48Ca+168,170Er systems that lead to the compound nuclei 216,218,220Ra*. A pronounced suppression of evaporation-residue production is observed for the more symmetric combinations, 48Ca+168,170Er. We relate this to the significant quasifission components already observed for these systems
The fusion-fission process in the reaction 34S+186W near the interaction barrier
No full textThe reaction S-34 + W-186 at E-lab=160 MeV was investigated with the aim of diving into the features of the fusion-fission process. Gamma rays in coincidence with binary reaction fragments were measured using the high efficiency gamma-ray spectrometer ORGAM at the TANDEM Accelerator facility of I.P.N., Orsay, and the time-of-flight spectrometer for fission fragments (FF) registration CORSET of the Flerov Laboratory of Nuclear Reactions (FLNR), Dubna. The coupling of the ORGAM and CORSET setups offers the unique opportunity of extracting details for characterizing the fusion-fission process and gives information regarding production of neutron-rich heavy nuclei. The FF-gamma coincidence method is of better use then the gamma - gamma coincidence method when dealing with low statistic measurements and also offers the opportunity to precisely correct the Dopler shift for in-flight emitted gamma rays.
Evidence of symmetric and asymmetric fission modes were observed in the mass and TKE distributions, occurring due to shell effects in the fragments. Coincident measurements allow for discrimination between the gamma rays by accepting a specific range within the mass distribution of the reaction products. Details regarding the experimental setup, methods of processing the acquisitioned data and preliminary results are presented
Uniconf: An alternative conformer generator with broad applicability
No full textThe Uniconf program aimed at conformational search/sampling in molecular clusters and isolated molecules with rotatable bonds has been developed. Unlike the other approaches, the spatial structural diversity of generated conformations is prioritized over targeting a semiempirical method or a force field minimum energy structures. The code is tested in generating of the gas-phase conformers for transition metal complexes, biologically active oligopeptides, and sodium ion microsolvated clusters. In one third of cases, either more or equally stable conformers compared to the previously found ones were generated. Energetically more diverse structures than available in the literature were obtained for practically all compounds.Prof. Vidar R. Jensen, University of Bergen, Norway, is deeply acknowledged for bringing our attention to the conformational search problem. The author gratefully acknowledges Prof. Luigi Cavallo, King Abdullah University of Science and Technology and Dr. Edrisse Chermak, SABIC, Saudi Arabia, and Dr. Arseniy A. Otlyotov, Dr. Daniil Itkis, Prof. Lada V. Yashina, and Andrey D. Moshchenkov, N. N. Semenov Federal Research Center for Chemical Physics RAS, Moscow, Russia for many insightful discussions. The anonymous reviewers of this work are gratefully acknowledged for their valuable comments and suggestions. The work was financially supported by the Russian Science Foundation (project 24-23-00301)
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